A. Field of the Invention
This invention relates to lighting systems, and components and assemblies for lighting systems, such as socket assemblies and lamp insulator assemblies, used in lighting systems. One aspect of an embodiment of the invention relates to fluorescent lamp sockets and mounting arrangements for such sockets, while another aspect relates to fluorescent lamp insulators and other aspects relate to lighting systems for refrigeration systems.
B. Related Art
The use and operation of fluorescent lighting systems are affected by a number of factors. One factor is safety, with one purpose being to minimize the possibility of electrical shock to personnel, including customers, maintenance personnel and the like. Another factor is the lighting system dimensions, including the lamp size, size of electrical contacts, and the positioning of electrical contacts. A further factor includes environmental considerations, such as the operating temperature, and the surrounding temperature. Environmental considerations also include humidity, especially where the surrounding temperature may result in moisture condensation or icing. Another consideration under the category of environment includes operating conditions such as vibration, impact, and protection from other mechanical factors. Another factor includes ease of installation, repair and replacement, including interchangeability or variability of parts and lamps in the lighting system. A further consideration is how the lighting system is electrically driven. Each of these factors will be discussed more fully below.
The majority of present lighting systems are electrically driven. Standards have been established for design, certification and approval of most lighting systems for the protection of personnel, such as building occupants, customers, installation and repair personnel, as well as others. Such standards include insuring that personnel are not exposed to high voltage or electric shock during installation or replacement of lighting elements such as lamps and bulbs. For example, most household incandescent bulbs have the hot and neutral contacts positioned relatively close to each other and installation of the bulb does not produce an exposed live contact. The risk of shock is minimized for the user by gasping the relatively low conductive glass portion of the bulb, and the contacts become live only after the bulb is substantially threaded into the socket. A common design for fluorescent sockets minimizes the possibility of electrical shock by having each end of the lamp inserted into respective sockets and seated or rotated a given amount before electrical contact occurs. This minimizes the possibility of having an exposed live contact. Another design of fluorescent sockets has one socket spring loaded so that the socket can be depressed with one end of the linear lamp inserted into the socket to permit enough spacing for the opposite end to be inserted into its respective socket. However, there is still a possibility that the opposite end of the lamp could be live before it is inserted into its corresponding socket. U-shaped fluorescent lamps and lamps having other shapes significantly different from the traditional linear shapes are comparable in some ways to traditional incandescent household bulbs in that the electrode contacts are closer together. As a result, the likelihood that shock may occur is somewhat reduced.
While incandescent lamps are generally driven off line voltage, fluorescent lamps typically require a ballast to start the lamp and regulate the power applied to the lamp. The voltage required to start the lamps depends on the lamp length and its diameter, with larger lamps requiring higher voltages. The ballast is designed to provide the proper starting and operating voltage required by the particular lamp. The ballast provides the proper voltage to fire the lamp and regulates the electric current flowing through the lamp to ensure stable light output. The ballast also supplies a correct voltage for the desired lamp operation and adjusts for voltage variations.
Traditionally, ballasts were of the electromagnetic, solid core type having a large transformer for providing the desired voltage and current. The voltage was typically provided to the lamp at or near the operating line voltage of 120 volts or 240 volts and frequency of 60 Hz or 50 Hz, respectively. Occasionally, the lamp is driven at a higher current in order to enhance the light output, but such overdriving of the lamp typically results in a shorter lamp lifetime.
Electronic or solid state ballasts provide greater energy efficiency by converting the power to light more efficiently than electromagnetic ballasts. Therefore, it is possible that an electronic ballast can provide a greater light output than an electromagnetic ballast with the same power consumption. The higher efficiency and light output is achieved by operating at a higher frequency than line frequency, and sometimes by operating at a higher voltage. As a result, it is possible that a ballast could acquire a relatively high open circuit voltage, as high as 750 volts, such as after lamp, ballast or other component failure, or some other electrical failure in the lighting system, which could consequently lead to injury or damage. For example, an improperly connected lamp in its respective sockets could lead to a high open circuit voltage, which in turn could cause arcing, over-heating, possible lamp failure and possible ballast failure.
Because of the higher driving voltages, the connection between the ballast and the lamp or bulb is important. Typically, fluorescent lamps have bi-pin contacts or double recessed contacts at each end of the fluorescent tube. The pins are separated by a predetermined center-to-center pin separation distance, which may vary according to the size of the lamp. For larger diameter lamps, the spacing can be larger for recessed double contact lamps such as some T10 and T12 lamps, but otherwise will be the same for bi-pin T8, T10 and T12 lamps. For example, a T12 double recessed contact lamp will have a larger center-to-center contact spacing than a T8 bi-pin lamp. The number 12 and the number 10 refer to the size, in eighths of an inch, of the lamp diameter.
Much of the hardware used with the T12 and T10 lamps have been relatively standardized. In one form of socket, commonly referred to as a tombstone socket (FIG. 23), the pins of each end of the lamp are inserted sideways into the socket until the lamp is centered in each socket. After being centered, the lamp is rotated about its longitudinal axis, allowing the pins to come into contact after rotation with the contacts in each socket. This socket minimizes the possibility of one end of the lamp being inserted into one socket with subsequent energtion of the lamp and the opposite free end being live. A shock could result from a live free lamp end.
In the tombstone style of socket, contact and illumination of the lamp is achieved by electrical contact between part of the outer surface of each pin and a portion of the surface of the contact. However, the electrical contact for each pin occurs only over a relatively small surface area, estimated to be in some circumstances about around 0.00360 to 0.00370 square inches. As a result, any high current through the lamp results in a relatively higher current density at the pins, that the socket may not have been designed for.
Another conventional socket for T10 and T12 lamps is a spring-biased recessed double contact socket, whereby one end of a lamp is inserted into the spring-biased socket, depressing the biased portion of the socket. Depressing the socket permits insertion of the opposite end of the lamp into the stationary socket on the fixture. However, nothing prevents the free end of the lamp from being live and a potential for electric shock. While this socket configuration may account for expansion and contraction due to thermal cycling and extreme environmental conditions, the potential for electric shock remains.
Bulb size also affects the safety and efficacy of lighting systems. The longer the fluorescent lamp, for example, the greater the current required to fire and maintain the lamp at the desired output. That greater current must be passed through the socket, across the socket conductors and to the pins of the lamp. With some socket designs, the current density may be relatively high between the socket and the pins for longer lamps. Consequently, overheating or other effects may occur.
Longer lamps also require a greater center-to-center distance between sockets. In conventional fixtures, the sockets are rigidly mounted to a fixed substrate that may contract or expand with changing environmental conditions. For example, in very low temperature situations such as out of doors or in freezer environments, the contraction could be a matter of sixteenths or eighths of an inch. For fixed sockets, such as tombstone-style sockets, the contraction over a large center-to-center distance between the sockets could force the sockets to bend away from the lamp (shown by the arrow 23A in FIG. 23), reducing the contact surface area between the socket and the lamp pins, as well as possibly disconnecting the lamp from the socket. In other fixtures where the sockets are mounted to a plastic substrate, portions of the plastic may flex or bend, permitting the socket to bend toward or away from the lamp, also possibly reducing the contact surface area between the socket and the lamp pins. Separation or disconnection of the lamp from the socket could cause arcing, overheating, or possible electric shock.
Conventional sockets leave portions of the lamp end exposed to environmental conditions. Such sockets generally engage the lamp pins through contacts recessed behind a flat face that butts against the flat end face of the bulb, from which the lamp pins extend. The abutting flat faces leave a gap, allowing contaminants, moisture, and cold air to enter the gap. Contaminants and moisture from cleaning or from use or maintenance may foul or corrode the connection and moisture may condense or freeze on the contacts of the connection. Additionally, cold air around the electrode area of the lamp will decrease the operating efficiency of the lamp, as well as possibly shorten the life of the lamp.
Environmental conditions affect the operation of lighting systems, for example, by decreasing operating efficiency, exposing the fixture to moisture, and extreme temperatures. Such conditions exist in outdoor illuminated signs, outdoor fixtures, unheated storage areas, refrigeration freezer cases and boxes, and cold storage rooms. Some systems see temperatures as low as xe2x88x9240xc2x0 F. and as high as 160xc2x0 F. Therefore, expansion and contraction may cause lighting system failure in many applications. Fixed center socket systems or spring-loaded socket systems often do not accommodate such changes in socket center-to-center distances caused by expansion and contraction of the substrate to which they are mounted. Temperature extremes affect the operation of the lamp by decreasing the operating efficiency. For example, some fluorescent lamps have peak operating efficiency at about 104xc2x0 F. Significant deviations from that temperature significantly decrease the efficiency of operation and output of the lamp. Higher temperatures may also contribute to overheating of the connection between the socket and the lamp. High humidity may subject the lamp-socket connection to condensation of moisture around the connection, and possibly icing about the lamp-socket connection. Consequently, the possibility of arcing or shorting may be increased. Increased moisture around the socket and lamp may also corrode the metal of the lamp-socket contacts, affecting the integrity of the connection between the lamp and the socket, for example by increasing the resistance in the connection, causing arcing which in turn may cause more corrosion or oxidation.
Additionally, operating conditions such as vibration and other physical forces, such as impact, affect lighting system operation. Vibration may cause the lamp and socket to disconnect, which also may cause premature lamp or ballast failure. Often, ballasts will fail immediately upon disconnection. Disconnection may also cause overheating, arcing, or more serious damage. Vibration is often caused by wind, nearby operation of motors or compressors, impact, such as by maintenance crews, earthquake and, in the case of refrigeration units, slamming doors, restocking of shelves, and heavy traffic. Vibration may cause vibration or rotation of the lamp in a socket, leading to disconnection, especially where there is nothing that inhibits disconnection.
During the manufacture of lighting fixtures, the sockets are not always accurately positioned to ensure optimum connection of the lamp pins and the sockets. For example, on tombstone-style sockets, fixedly mounting the socket on the substrate several sixteenths or an eighth of an inch too close together or too far apart could lead to an improper connection. If the sockets are too close together, installing the lamps between the sockets will force one or both sockets to bend away from the lamp. Bending could cause either a poor connection or an incomplete connection with the lamp, especially where there is nothing in the tombstone socket design that inhibits disconnection in a direction longitudinally of the lamp. If one socket has a good connection, but the other socket has a poor connection or no connection at all, the affected lamp end will be live and subject to arcing or overheating and possible damage or injury. Thereafter, replacement of lamps would result in further loosening of the sockets and possible failure of the fixture.
In addition to sockets not always being properly positioned or spaced, an inadequate or failed connection can result where lamp lengths vary from one lamp to the next, or between lots. The length of one lamp may vary by a sixteenth of an inch of more from the length of another lamp of the same type merely because of manufacturing tolerances that are too large. Variations in nominal lamp length could cause properly positioned sockets to bow outwardly upon installation of the lamp. Shorter lamps may lead to inadequate connection.
Poor socket-lamp connection can also result from poor contact aligmnent on lamps. For bi-pin fluorescent lamps, for example, a pair of spaced apart contact pins are positioned at each end of the lamp. For proper lamp connection, each pair of pins must properly engaged the associated sockets. Since the sockets are mounted to a substrate or support surface, the alignment of the contacts in each socket is relatively fixed. However, if the pin alignment of one pair is not identical to the pin alignment of the pair of pins on the opposite end of the lamp, an incomplete connection may result at one end or the other of the lamp. Failure to contact, or an incomplete contact may result in possible failure of the fixture.
Repair or replacement of lighting fixtures is often difficult in cases where the sockets are fixedly mounted to a substrate. Often, the substrate is not designed for easy removal and replacement of lighting sockets, further exacerbating any connection problems that might occur between lamps and sockets. Similar comments may apply in situations where lamps are first installed or are replaced, and where sockets are jammed or impacted during lamp removal or replacement. Loose or bent sockets increase the likelihood of connection failure. Similar problems could arise during cleaning or maintenance of the equipment surrounding the lighting fixture. For example, in refrigeration units, the lamp fixture could be jarred or jammed during cleaning, restocking of shelves or at other times. Additionally, sockets may be jarred or damaged when they are first installed in the support structure, when lamps are first installed in the fixture, or when lamps are removed and replaced. In these circumstances, it is possible that the connection between the socket and the lamp is no longer adequate, resulting in or leading to inadequate or incomplete connection or a failed connection.
It is also believed that inadequate connection and reduced conductivity in the lighting circuit may lead to lighting inefficiencies and possible ballast failure even before complete failure of an electrical connection, such as failure of the connection between the lamp and its socket. It is believed that the effect on the ballast of an inadequate connection results from a combination of the characteristics of the ballast and the characteristics of the lighting circuit. These characteristics will be discussed more fully below.
Electronic ballasts used to drive fluorescent lamps are constant current devices. The lamps they are intended to drive are designed to operate at a relatively constant current to ensure the desired electron and photon production in the lamp. If, for some reason, the impedance of the lamp increases, the current will decrease unless the ballast maintains the current constant. Any increased resistance or impedance in the lamp circuit as seen by the ballast will typically result in a higher voltage across the ballast output terminals. Therefore, differences (or variances)in the lighting circuit from the optimum design will also affect the ballast and ballast operation, in addition to affecting the other components of the circuit. These changes may occur over time, such as by lamp aging, by changes in the socket-lamp connection, such as corrosion, by contact separation, by contact icing or corrosion and the like. These differences may also be inadvertently incorporated in the lighting circuit from the beginning. For example, differences may arise such as through an inadequate lamp connection resulting from an oversized lamp, improper socket placement, socket damage during installation, as well as other reasons. For example, if a high voltage is applied across an inadequate connection arcing may occur, resulting in oxidation and higher contact resistance and lower conductivity. The higher resistance produces a larger impedance in the circuit as seen by the ballast, which would then cause the ballast to adjust accordingly.
Lower conductivity, as well as other differences or changes in the circuit from the optimum design, may lead to ballast overheating, as well as overheating of other circuit components, and possibly ballast or other circuit failure.
Many conventional lamp fixtures use sockets dimensioned for only T10 and T12 sized lamps. However, newer T8 and T5 lamps are not interchangeable with T10 and T12 lamps, nor with each other. Therefore, interchangeability of sockets is made more difficult and interchangeability of lamp sizes for a given socket arrangement is not available. Consequently, the drawbacks discussed previously relating to replacement of sockets apply equally to interchanging one socket size or type for another.
For example, T8 and T5 fluorescent lamps would use different lighting fixtures under conventional designs. Some of those fixtures may have marginal lamp pin-to-pin socket terminal connections that may cause premature lamp failure, ballast burnout, and the like. Additionally, differences in lamp length between T8 and T5 lamps make conventional fixtures difficult to use and precluding interchangeability of lamps with having to replace fixtures. The nominal lengths for T8 lamps are 72 inches, 60 inches, 48 inches, 36 inches and 24 inches. The nominal lengths for T5 lamps are in standard metric lengths, corresponding to 57.05 inches, 45.24 inches, 33.43 inches, and 21.61 inches. Therefore, changing from T8 to T5 lamps requires a change of fixtures. Additionally, the lamp pin center-to-center spacing is different, being 0.490 for the T8 lamp and 0.185 for the T5 lamps.
Embodiments of a lighting system and components are described which minimize the possibility of electric shock due to incomplete lamp and socket connection, or due to complete electrical disconnect between a lamp and a socket connection, possibly causing a high open circuit voltage and/or ballast and component overheating or failure. Embodiments are also described which minimize the possibility of contamination due to cleaning procedures in equipment surrounding lighting fixtures, maintenance procedures, repair and replacement procedures, and the like. Elements are also described which provide enhanced thermal protection for more efficient lamp operation and regulation, and protect the lamp and socket connection from environmental factors, such as temperature extremes, humidity, condensation, icing and vibration. A further aspect of a lighting system and components described herein improves the construction and the procedures used in the installation, repair and replacement of lighting fixtures, and provides for a greater flexibility in, and interchangeability of, lighting elements. A further aspect of a lighting system described herein improves the operating characteristics of the lighting system, for example by decreasing the operating temperature of the ballast and/or associated components in some instances, by reducing the occurrence of ballast failure, lamp failure, component failure or of other problems in those components or by improving the light output. Elements are also described which provide a better matched lighting circuit which is less likely to lead to circuit breakdown or failure. These benefits can be achieved even at higher voltages provided by some ballasts.
In one embodiment of the invention described, a socket is provided which permits connection between the socket and the lamp that is less dependent on the specific mounting arrangement or holder, or on its positioning. Preferably, the socket and its connection to the lighting element are moveable relative to the particular mounting arrangement. The sockets described herein can be positioned at one or both ends of the lighting element, such as a fluorescent lamp. In one aspect, they are intended to be considered more a part of the lamp than of the substrate from which the socket is supported, because the socket-lamp configuration is believed to be more significant than the particular form of the socket-substrate connection. Embodiments of the disclosed lighting system permit variants of pin alignments and lamp lengths, lamp interchangeability and provide for better support of the lamp. Several embodiments of the design also permit installation of at least two different sizes of lamps, both in terms of diameter and lamp length. Embodiments of the described invention are also particularly suited for use with solid state ballasts.
For example in one preferred aspect of the present invention, a socket includes a housing with at least one cylindrical, slotted or female-type connector and a cavity or enclosure for accepting a lamp into the socket. This configuration can be used with present bi-pin lamps where the lamp is inserted into the socket, and permits various other benefits, such as being able to protect the lamp, provide support for the lamp and to have a more stable electrical lamp connection. Preferably, the connector extends into the cavity or enclosure a distance less than the full length of the enclosure and may even be flush with the bottom of the enclosure, for example to permit greater insertion of the lamp in the socket if desired on the one hand, or to reduce the size of the enclosure on the other hand. Preferably the connector is one that engages, surrounds and contacts all or a significant portion of the pin that it connects to for ensuring the maximum connection surface area possible and improving conductivity.
In accordance with another aspect of the present invention, a socket is described for a lighting system wherein the socket has a socket body and an electrical connector, and further includes protection for the lighting element such as a lamp. The protection may take the form of electrical insulation, thermal insulation, protection from vibration, contamination, and the like. In one form of the invention, the protection is provided by a cover for the conductor portion of the lamp. In another form of the invention, the protection is provided by a cover that extends over the conductive end of the lamp, and in still another form, the protection is provided by a seal between the socket and the lamp.
For example, in accordance with one preferred aspect of the present inventions, a socket is described for a lighting system wherein the socket includes an element for forming a seal between the socket body and the lighting element. The seal can be formed from an O-ring or other suitable seal element. A seal can provide protection from the effects of the environment, including humidity, temperature extremes, as well as particulate and other contamination. A seal can also protect the lighting system from the effects of vibration, impact, and other external forces. In one preferred form of the invention, the socket covers and seals a portion of the lamp, for example to provide thermal insulation to the electrode area of the lamp.
In another form of the invention, the contact includes a plurality of contacts in a base of the socket. For example, the contacts can be arranged in a diamond- or cross-configuration where two contacts accommodate the pins of one size of lamp, and wherein two other contacts accommodate the pins of a differently-sized lamp. Such an arrangement could accommodate a T8 sized lamp, as well as a T5 sized lamp, a T8 and a T10 or T12, or any combination of known lamp configurations. The particular contact arrangement provides for the optimum isolation between adjacent contacts and between neutral and hot contacts.
In another form of one aspect of the inventions, the socket, such as the external surface of the socket body, may include one or more grooves or other elements for accepting a removable clip or mounting attachment, to mount the socket to a substrate or other support. In one embodiment, the groove would be approximately the same size as the mounting element at one end of the lamp, and larger than the corresponding dimension of the mounting element at the other end of the lamp. This arrangement permits expansion and contraction of the fixture relative to the fixed length of the lamp. Alignment indicators may also be included to indicate the desired lamp pin aligmnent relative to the socket.
In an additional form of another aspect of the inventions, a socket includes an electrical connector and a body extending longer than the contact length of the connector and wherein the connector or other portion of the socket includes a structure for engaging an insulator or protector on the lamp. The structure may include barbs, points, or other elements for establishing an interference contact with the insulator. For example, connection between the lamp pins and socket can be achieved by a split sleeve slotted terminal made from spring material in the socket. The slotted terminal has an I.D. that is smaller than the O.D. of the male lamp pin, providing a pressure fit, which pressure fit provides a safeguard against accidental disconnection caused by vibration and the like. To further safeguard against such disconnection, two pointed barbs preferably extend outwardly from the external surface of the slotted terminal and engage the inner surface of counterbores of the lamp insulators. In addition, the socket""s O-ring seal provides for a gripping of the exterior surface of the lamp which serves as added protection against disconnection.
In a further form of the inventions, a socket is provided for a lighting assembly having a socket body and at least one electrical connector, and a holder for the socket body which is movable, at least rotatably or slidably, relative to the socket body, to permit expansion or contraction of the fixture assembly relative to the fixed lamp dimension. Preferably, the holder is removable from the socket. In another form of the invention, the holder is spring-biased and the mounting surface for mounting the holder to the substrate includes a track for adjusting the position of the holder relative to the socket.
In a further aspect of the inventions, a protector in the form of an insulator is provided for such lighting elements as fluorescent lamps, wherein the insulator protects at least one of the conductors on the lamp and engages the conductor in such a way that removal of the insulator is inhibited. For example, with a bi-pin fluorescent lamp, the insulator may include two openings corresponding to the pins and dimensioned in such a way as to provide an interference fit between each pin and the opening in the insulator. In one preferred form of the invention, the height of the insulator is greater than or equal to the length of the pins to protect the pins. In another form, the insulator also covers a portion of the lamp body in order to help protect or insulate the lamp end.
In another aspect of the invention, a lamp assembly is provided including a lamp with at least one contact extending from a surface of the lamp for receiving and supplying electrical energy to the lamp and a contact protector extending substantially around the contact in such a way that the contact is still accessible for electrical contact. In one form of the invention, the lamp is a bi-pin lamp wherein the two pin contacts are preferably cylindrical and the contact protector extends around both pins while leaving sufficient space to be accessible for electrical connection. The protector is preferably an insulator which extends beyond the ends of the pins so that the pins are recessed within the insulator.
In still another form of the invention, pin extenders are placed over respective pins on the lamp and hold the insulator in place. The pin extenders may also enhance the ability to make a reliable connection with a socket of the type disclosed herein. In a further form of the invention, the lamp and the conductive contacts are separated by an insulator between the contacts such that the shortest, unobstructed distance between the contacts is no less than 0.50 inch.
In another form of the invention, a connector is provided for connecting the contacts of a fluorescent light source to a source of electrical energy including an input conductor for receiving electrical energy from a ballast and an output conductor adapted to accept a contact of a fluorescent light source. An electrical circuit is provided between the input and the output conductors for passing current from the input conductor formed in such a way as to improve the conductivity in the circuit. It is preferred that the use of a connector having one or more of these characteristics can be used in a refrigeration system, such as a refrigerated display case wherein any contact resistance or contact surface area between the connector and the fluorescent light source remains substantially the same over a broad temperature range, for example from minus 20 degrees Fahrenheit to 70 or 100 degrees Fahrenheit and under the conditions encountered in refrigerated display cases. Such display cases encounter temperature and moisture extremes, and vibration, impact and other environmental conditions. They also experience a number of electrical influences, such as noise from other equipment such as compressors, and the like, line excursions and other variations. The lighting system of the present inventions and the components thereof can withstand many and preferably all of these conditions, and permits the lighting circuit to have a wider range of tolerance in the conditions within which it can operate.
In another form of the invention, a connector is provided having contacts for coupling to a fluorescent lamp where the contacts of the connector corresponding to the contacts on the lamp are separated from each other by an unobstructed surface path no less than 0.50 inch. Preferably, a substantially nonconductive barrier extends between the contacts on the connector to provide part of the separation. In one configuration, the contacts are cylindrical split contacts for accepting pins on a bi-pin lamp, and the contacts are enclosed by plastic sleeves to inhibit arcing between the contacts. Preferably, the contacts are recessed below the open ends of the respective sleeves.
In an additional form of the invention, a circuit for lighting a lamp is provided including an electronic ballast, a lamp socket for supplying electrical energy to a lamp through contacts in a socket and at least one electrical conductor for coupling the ballast to the socket. A junction between the conductor and the contact of the lamp has a contact surface area of at least 0.005 square inch and preferably at least 0.008 and 0.01 or 0.10 square inch or more, to ensure improved conductivity, both electrical and thermal, across the junction.
These and other aspects of the present invention will be understood more fully after consideration of the drawings, a brief description of which is provided below, and the detailed description of the preferred embodiments.